1. Field
The present disclosure relates generally to power converters and, more specifically, to power converters utilized with dimmer circuits.
2. Related Art
Residential and commercial lighting applications often include a dimming functionality to provide variable light output. One known technique for providing this function is phase-angle dimming, which may be implemented using either leading-edge or trailing-edge phase-control. A semiconductor switch-based circuit (e.g., TRIAC or MOSFET) is often used to perform this type of phase-angle dimming and operates by delaying the beginning of each half-cycle of alternating current (ac) power or trimming the end of each half-cycle of ac power. By delaying the beginning of each half-cycle or trimming the end of each half-cycle, the amount of power delivered to the load (e.g., the lamp) is reduced, thereby producing a dimming effect in the light output by the lamp.
It is often convenient to designate the position of the TRIAC dimmer circuit and the resultant amount of power delivered to the load in terms of a fraction of the period of the ac input voltage measured in degrees. In general, the ac input voltage is a sinusoidal waveform and the period of the ac input voltage is referred to as a full line cycle. As such, half of the period of the ac input voltage is referred to as a half line cycle. An entire period has 360 degrees, and a half line cycle has 180 degrees. Typically, the phase-angle is a measure of how many degrees (from a reference of zero degrees) of each half line cycle are disconnected by the TRIAC dimmer circuit. For example, removal of half of the ac input voltage in a half line cycle by the TRIAC dimmer circuit corresponds to a phase-angle of 90 degrees. In another example, removal of a quarter of the ac input voltage in a half line cycle may correspond to a phase-angle of 45 degrees. On the other hand, the conduction angle is a measure of how many degrees (from a reference of zero degrees) of each half line cycle that are not disconnected by the TRIAC dimmer circuit. In other words, the conduction angle is a measure of how many degrees of each half line cycle in which the TRIAC dimmer circuit is conducting. In one example, the removal of a quarter of the ac input voltage in a half line cycle may correspond to a phase-angle of 45 degrees and a conduction angle of 135 degrees.
Although phase-angle dimming works well with incandescent lamps that receive the altered ac input voltage directly, it typically creates problems for light emitting diode (LED) lamps that are often driven by regulated power converters. The regulated power converters are used to provide the LED lamps with a regulated current and voltage from the altered ac power line. However, conventional power converters often produce non-ideal results when used with TRIAC dimmer circuits. As a result, flickering or shimmering of the LED lamp can occur at large conduction angles and flashing of the LED lamp can occur at low conduction angles.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present disclosure. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present disclosure.